Engine management strategy

Abstract

A system and method for controlling a vehicle to implement an engine torque management strategy. The engine torque management strategy implements a sophisticated engine knock control method that alleviates/mitigates the cause of the knock while also optimizing vehicle performance and engine efficiency without compromising engine hardware protection. Whenever suitable, the system and method attempt to reduce the amount of air trapped in a knocking cylinder to reduce its effective compression ratio and to eliminate the knock while keeping the same optimal spark timing for combustion efficiency.

What is claimed is:  
     
       1. A method of controlling an engine system of a vehicle, the engine system including an engine having a plurality of cylinders, the method comprising:
 detecting, at a processor, engine knock in at least one cylinder of the plurality of cylinders; 
 calculating, at the processor, knock density for each cylinder in which engine knock was detected, each knock density being indicative of an intensity of the detected engine knock in a corresponding cylinder; 
 for each cylinder in which engine knock was detected:
 based on expected engine torque losses, determining, at the processor, whether to perform spark retardation or airflow reduction to decrease the engine knock in the cylinder, and 
 based on the determining, performing, by the processor, spark retardation or airflow reduction for the cylinder, the airflow reduction being proportional to the cylinder's calculated knock density; and 
 
 for each cylinder in which engine knock was not detected:
 increasing, by the processor, airflow into the cylinder. 
 
 
     
     
       2. The method of  claim 1 , wherein reducing air in each cylinder in which engine knock was detected and increasing air in each cylinder in which engine knock was not detected comprises adjusting at least one of a throttle and corresponding intake valves associated with the respective cylinders. 
     
     
       3. The method of  claim 1 , further comprising:
 determining, at the processor, whether the air increase in a cylinder in which engine knock was not detected has reached a maximum level; and 
 in response to determining that the air increase in the cylinder in which engine knock was not detected has reached the maximum level, clipping the air increase to the maximum level and calculating a remaining knock density. 
 
     
     
       4. The method of  claim 3 , further comprising performing spark retardation based on the remaining knock density. 
     
     
       5. The method of  claim 1 , further comprising determining whether at least one of airflow reduction or airflow increase can be performed based on a calibration setting. 
     
     
       6. The method of  claim 5 , further comprising, when spark retardation is determined to be performed based on engine torque losses, controlling spark retardation to mitigate engine knock in each cylinder in which engine knock was detected in response to determining that airflow reduction cannot be performed based on the calibration setting. 
     
     
       7. The method of  claim 1 , further comprising:
 determining, at the processor, whether engine knock has been detected for all of the plurality of cylinders; and 
 when spark retardation is determined to be performed based on engine torque losses, controlling spark retardation in response to determining that engine knock has been detected for all of the plurality of cylinders. 
 
     
     
       8. The method of  claim 1 , further comprising determining, by the processor, an amount of air increase for a non-knocking cylinder based on:
 (i) a delta air increase in the non-knocking cylinder, 
 (ii) a delta air reduction in a knocking cylinder, 
 (iii) a spark torque efficiency in the non-knocking cylinder, and 
 (iv) a spark torque efficiency in the knocking cylinder. 
 
     
     
       9. The method of  claim 8 , wherein the amount of air increase for the non-knocking cylinder is determined using the following equation: 
       
         
           
             
               
                 
                   Δ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     M 
                     pernonknocking 
                   
                 
                 = 
                 
                   
                     ΣΔ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       M 
                       perknocking 
                     
                     * 
                     ρ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       spk 
                       knocking 
                     
                   
                   
                     Σρ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       spk 
                       nonknocking 
                     
                   
                 
               
               , 
             
           
         
       
       where ΔM pernonknocking  is the delta air increase in the non-knocking cylinder, ΔM perknocking  is the delta air reduction in the knocking cylinder, ρspk nonknocking  is the spark torque efficiency in the non-knocking cylinder, and ρspk knocking  is the spark torque efficiency in the knocking cylinder. 
     
     
       10. An engine torque management system of a vehicle including an engine having a plurality of cylinders, the system comprising:
 at least one knock sensor associated with at least one cylinder of the plurality of cylinders; and 
 a controller connected to the at least one knock sensor, the controller being configured to:
 detect engine knock in at least one cylinder of the plurality of cylinders; 
 calculate knock density for each cylinder in which engine knock was detected, each knock density being indicative of an intensity of the detected engine knock in a corresponding cylinder; 
 for each cylinder in which engine knock was detected:
 based on expected engine torque losses, determine whether to perform spark retardation or airflow reduction to decrease the engine knock in the cylinder, and 
 based on the determination, perform spark retardation or airflow reduction for the cylinder, the airflow reduction being proportional to the cylinder's calculated knock density; and 
 
 for each cylinder in which engine knock was not detected:
 increase airflow into the cylinder. 
 
 
 
     
     
       11. The system of  claim 10 , wherein the controller is configured to reduce air in each cylinder in which engine knock was detected and increase air in each cylinder in which engine knock was not detected by adjusting at least one of a throttle and corresponding intake valves associated with the respective cylinders. 
     
     
       12. The system of  claim 10 , wherein the controller is further configured to:
 determine whether the air increase in a cylinder in which engine knock was not detected has reached a maximum level; and 
 in response to determining that the air increase in the cylinder in which engine knock was not detected has reached the maximum level, clip the air increase to the maximum level and calculate a remaining knock density. 
 
     
     
       13. The system of  claim 12 , wherein the controller is further configured to perform spark retardation based on the remaining knock density. 
     
     
       14. The system of  claim 10 , wherein the controller is further configured to:
 determine whether at least one of air reduction and air increase can be performed based on a calibration setting. 
 
     
     
       15. The system of  claim 14 , wherein the controller is further configured to, when spark retardation is determined to be performed based on engine torque losses, control spark retardation to mitigate engine knock in each cylinder in which engine knock was detected in response to determining that air reduction cannot be performed based on the calibration setting. 
     
     
       16. The system of  claim 10 , wherein the controller is further configured to:
 determine whether engine knock has been detected for all of the plurality of cylinders; and 
 when spark retardation is determined to be performed based on engine torque losses, control spark retardation in response to determining that engine knock has been detected for all of the plurality of cylinders. 
 
     
     
       17. The system of  claim 10 , wherein the controller is further configured to determine an amount of air increase for a non-knocking cylinder based on:
 (i) a delta air increase in the non-knocking cylinder, 
 (ii) a delta air reduction in a knocking cylinder, 
 (iii) a spark torque efficiency in the non-knocking cylinder, and 
 (iv) a spark torque efficiency in the knocking cylinder. 
 
     
     
       18. The system of  claim 17 , wherein the amount of air increase for the non-knocking cylinder is determined using the following equation: 
       
         
           
             
               
                 
                   Δ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     M 
                     pernonknocking 
                   
                 
                 = 
                 
                   
                     ΣΔ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       M 
                       perknocking 
                     
                     * 
                     ρ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       spk 
                       knocking 
                     
                   
                   
                     Σρ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       spk 
                       nonknocking 
                     
                   
                 
               
               , 
             
           
         
       
       where ΔM pernonknocking  is the delta air increase in the non-knocking cylinder, ΔM perknocking  is the delta air reduction in the knocking cylinder, ρspk nonknocking  is the spark torque efficiency in the non-knocking cylinder, and ρspk knocking  is the spark torque efficiency in the knocking cylinder.